Calcium is the most abundant mineral in the human body. Of the body's total calcium, about 99% is in the bones and teeth where it plays a structural role. The remaining 1% is present in body tissues and fluids where it is essential for cell metabolism, muscle contraction and nerve impulse transmission.
About Calcium, Calcium Sources, Calcium Rich Foods & Calcium's Role In The Body
The main function of calcium is structural. The skeleton of a young adult male contains about 1.2 kg of calcium. There is continuous movement of calcium between the skeleton and blood and other parts of the body. This is finely controlled by hormones. Hormones regulate calcium deposits and calcium removal from the body's bones.
Calcium also plays a role in cell biology. Calcium can bind to a wide range of proteins altering their biological activity. This is important in nerve impulse transmission and muscle contraction. Calcium is also needed for blood clotting, activating clotting factors.
Vitamin D is needed for absorption of dietary calcium and so calcium deficiency may be linked with rickets in children. In adults, calcium deficiency may lead to osteomalacia (softening of bones). This may be related to repeated pregnancy with lengthy breast feeding.
Osteoporosis can be due to calcium deficiency. This involves loss of calcium from the bones and reduced bone density. This causes bones to be brittle and liable to fracture. Bone loss occurs with age in all individuals. This usually occurs after 30-40 years and involves the shrinking of the skeleton. Bone loss is greatest in women following the menopause. This is due to reduced levels of the hormone, estrogen. Postmenopausal women are particularly at risk from osteoporosis.
Some research has indicated vegetarian women are at less risk of osteoporosis than omnivorous women. This is thought to be due to animal protein increases calcium loss from bones. However, other research has found no difference between vegetarians and omnivores.
The risk of osteoporosis may be altered by factors other than diet. Lack of exercise, being underweight, smoking and alcohol usage can all increase the risk.
A low level of calcium in the blood and tissues can cause hypocalcaemia. This involves sensations of tingling and numbness and muscle twitches. In severe cases muscle spasms may occur. This is called tetany. It is more likely to be due to a hormonal imbalance in the regulation of calcium rather than a dietary deficiency.
Excess calcium in the blood can cause nausea, vomiting and calcium deposition in the heart and kidneys. This usually results from excessive doses of vitamin D and can be fatal in infants.
Dietary Calcium Sources, Calcium Rich Foods
Calcium is present in a wide range of foods. Calcium rich foods include dairy products, leafy green vegetables, nuts and seeds (almonds, brazils, sesame seeds), tofu, and dried fruit. Another calcium source is cereal, since most flour is fortified with calcium carbonate. Hard water may also provide a minimal amount of calcium. Meats in general are NOT calcium rich foods.
Calcium balance can be affected by a range of other factors. Vitamin D is essential for absorption of calcium from the gut. This is because calcium is transported into the body by a special carrier protein which requires vitamin D for its synthesis.
A number of substances can inhibit the absorption of calcium. Phytic acid, found in bran, whole cereals and raw vegetables is one of these. Uronic acid, a component of dietary fibre, and oxalic acid, found in certain fruits and vegetables can also bind calcium. However, diets habitually high in these acids are not thought to have a major effect on calcium absorption. Saturated fats can also lessen calcium absorption.
Calcium is lost in the feces, urine and sweat. Calcium loss is reduced if dietary calcium is low. Adaptation to both high and low calcium intakes occur. Reduced intake leads to increased efficiency of absorption. In infants and children calcium is retained for new bone growth. Calcium is also lost during lactation in breast milk. Eating calcium rich foods is one way to increase calcium deposit and combat calcium loss.
|Sources of Calcium (single servings)|
|Good Calcium Sources
||Fair Calcium Sources
||Poor Calcium Sources
|Tofu (60g or 2oz)
||Brown bread (2 slices)
||Spaghetti, boiled (100g or 3Żoz)
|Cheddar cheese (slice, 40g)
||Brazil nuts (9 nuts, 30g)
||Brown rice (190g or 8oz)
|Cows milk (0.3 pint)
||Dried apricots (8 apricots)
|Spinach, boiled (130g or 5oz)
||French beans, boiled (100g)
|Dried figs (4 figs)
||Cottage cheese (45g or 1Żoz)
|Soya cheese (slice, 40g)
||Sesame seeds (15g or Żoz)
|Chick peas, boiled (200g or 8oz)
|Baked beans (200g or 8 oz)
|Broccoli, boiled (95g or 3Żoz)
The old Recommended Daily Amounts (RDAs) have now been replaced by the term Reference Nutrient Intake (RNI). The RNI is the amount of nutrient which is enough for at least 97% of the population.
The average female needs a minimum of 700mg of calcium a day. If you are breast feeding or post-menopause, it is recommended that you intake 1250mg a day.
However, note that an excessive amount of calcium may lead to calcium deposits.
During pregnancy, calcium absorption from the gut increases and no additional calcium is generally needed. Pregnant adolescents are an exception to this, having particularly high calcium needs.
Breast feeding women need an extra 550 mg of calcium. A lactating women can lose up to 300 mg a calcium/day in breast milk.
Calcium absorption decreases with age so it is important the elderly have adequate dietary calcium.
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